1. Field of the Invention
The invention relates to a thin-walled circular-shaped metal structure and a method of fabricating the same, and more particularly to such a metal structure usable as a photosensitive drum or a fixing roller in an electrophotographic printer or copier, and a method of fabricating the same.
2. Description of the Related Art
For instance, in accordance with Japanese Unexamined Patent Publication No. 10-10893, a film of which a photosensitive drum or a fixing drum used in a conventional electrophotographic printer and copier is fabricated is composed generally of organic material such as polyimide or a metal as inorganic material, such as iron, aluminum, stainless steel and nickel.
The above-mentioned film is required to have a thickness in the range of 0.03 to 0.20 mm as a practical thickness. However, such a thickness can be accomplished only by a film composed of polyimide or nickel. For instance, a nickel film having such a thickness can be fabricated by electrocasting.
It is generally said that a fixation section consumes about 80% of power to be totally consumed in an electrophotographic printer or copier. In addition, power consumption depends greatly on a material of which a fixing roller or a fixing film is composed.
For instance, if a fixing roller or film is composed of polyimide, an organic material, having a thermal conductivity {fraction (1/510)} to {fraction (1/40)} smaller than a thermal conductivity of the above-mentioned iron, aluminum, stainless steel or nickel, it would be necessary to heat a fixing roller or film much time until the fixing roller or film become workable. A period of time in which a fixing roller or film is heated is a time in which a user has to wait after a printer or copier has been turned on until the printer or copier becomes workable. Since a user usually desires a printer or copier to become workable as soon as possible, a fixing roller or film has to be heated even when the printer or copier is not in use, resulting in an increase in power consumption.
On the other hand, if a fixing roller or film is composed of nickel having a thermal conductivity 210 times greater than that of polyimide, it would be necessary to heat a fixing roller or film less time than a time during which a polyimide film has to be heated, until the fixing roller or film become workable. As a result, it is no longer necessary to heat a fixing roller or film to heat in advance, and hence, a printer or copier including the fixing roller or film composed of nickel becomes workable immediately when the printer or copier is turned on.
As mentioned above, power consumption in a printer or copier can be reduced by using a nickel film as a fixing film. However, a conventional method of fabricating a nickel film is accompanied with problems as follows.
As mentioned earlier, a nickel film having a thickness of 0.03 to 0.20 mm is fabricated by electrocasting. That is, such a nickel film is fabricated by precipitating nickel ions by electrolysis. Hence, the thus fabricated nickel film has such a columnar crystal structure as illustrated in FIG. 7, and resultingly, has a shortcoming that the nickel film is weak to a mechanical repeated stress.
In addition, in accordance with a fatigue test, the nickel film has a lifetime in the range of a couple of tens thousand rotation to a couple of millions rotation. There is much dispersion in a lifetime of a nickel film.
In particular, a nickel film fabricated by electrocasting shows remarkable thermal embrittlement when heated to a temperature over 200 degrees centigrade. Hence, a nickel film fabricated by electrocasting is not suitable as a fixing film.
Though ions can be readily precipitated out of a pure metal by electrocasting, it is almost impossible to precipitate ions out of an alloy such as a stainless steel.
As another method of fabricating a metal cylindrical film, there has been suggested a method including the steps of rounding a thin film having a thickness in the range of 0.03 to 0.20 mm, and welding the thus rounded film into a cylinder-shaped film. According to this method, any metal may be used for fabricating a metal cylindrical film.
However, this method is accompanied with such a problem of shortage in a mechanical strength and non-uniformity in a shape of a cylinder, due to a bead treatment at a welded portion, and further due to a defect in a welded portion with respect to a metal structure. In addition, since a metal cylindrical film is fabricated in the method by splicing thin films to each other, a skill is required and it takes much time to do so, resulting in an increase in cost and absence of mass-productivity. Hence, the method is not put to practical use yet.
In view of the above-mentioned problems in the conventional method of fabricating a metal cylinder film, it is an object of the present invention to provide a circular-shaped metal structure such as a metal cylinder film which has a sufficient mechanical strength and lifetime, and is suitable for mass-production.
It is also an object of the present invention to provide a method of fabricating such a circular-shaped metal structure.
It is further an object of the present invention to provide an apparatus of fabricating such a circular-shaped metal structure.
In one aspect of the present invention, there is provided a circular-shaped metal structure fabricated by plastic working and having a thickness equal to or smaller than 0.09 mm.
In the specification, the term xe2x80x9ccircular-shaped metal structurexe2x80x9d covers a structure composed of a metal, having a closed cross-section in a direction perpendicular to an axis thereof, and being in the form of a loop. For instance, a typical circular-shaped metal structure is a metal cylinder. A belt, a sleeve, a pipe and the like are all included in a circular-shaped metal structure.
The circular-shaped metal structure may include a seam extending in an axis-wise direction thereof. However, it is preferable that the circular-shaped metal structure includes no seams extending in an axis-wise direction thereof.
In the above-mentioned circular-shaped metal structure, a reduction rate of a thickness of the circular-shaped metal structure after plastic-worked to a thickness of the circular-shaped metal structure before plastic-worked is equal to or greater than 40%.
It is preferable that the circular-shaped metal structure has a Vickers hardness Hv equal to or greater than 380 after plastic-worked.
It is preferable that the circular-shaped metal structure has a Vickers hardness Hv in the range of 100 to 250 both inclusive after plastic-worked and then annealed.
For instance, the above-mentioned circular-shaped metal structure is fabricated by spinning working. However, the circular-shaped metal structure can be fabricated by plastic working other than spinning.
In another aspect of the present invention, there is provided a method of fabricating a circular-shaped metal structure, including the steps of (a) rotating a pipe around an axis thereof, the pipe being composed of a plastic-workable metal, and (b) applying drawing to an outer wall of the pipe with the pipe being kept rotated, to reduce a wall thickness of the pipe and lengthen a wall of the pipe.
In accordance with the method, it is possible to fabricate a circular-shaped metal structure which may be used as a photosensitive drum or a fixing roll by applying spinning working to a pipe. Herein a pipe includes a pipe having a bottom and a pipe having no bottom. A pipe having a bottom can be fabricated by warm or cold drawing, and a pipe having no bottom can be fabricated by rounding a film and welding the film at opposite ends. The pipe is annealed to control a hardness thereof, if necessary, and then, is subject to spinning to have a thickness in the range of 0.03 to 0.20 mm both inclusive. Then, if necessary, the pipe is annealed again at a low temperature. The resultant circular-shaped metal structure is stiff, has a high resistance to fatigue and a high thermal conductivity, and is superior as a photosensitive drum or a fixing drum.
Table 1 shows comparison in performances between a thin-walled circular-shaped metal structure fabricated in accordance with the above-mentioned method and a thin-walled circular-shaped metal structure fabricated in accordance with drawing as a conventional method. It is assumed in Table 1 that a circular-shaped metal structure is used as a fixing roller.
In Table 1, a column xe2x80x9cAxe2x80x9d indicates a uniformity in a thickness, a column xe2x80x9cBxe2x80x9d indicates a straightness, a column xe2x80x9cCxe2x80x9d indicates a hardness, and a column xe2x80x9cDxe2x80x9d indicates a total estimate. A circle (◯) in the columns A, B and C indicates that the circular-shaped metal structure passes the test, and a cross (X) in the columns A, B and C indicates the circular-shaped metal structure cannot pass the test.
For instance, a circular-shaped metal structure having a thickness of 0.09 mm, fabricated in accordance with the present invention, passes the tests with respect to a uniformity in a thickness, a straightness and a hardness, whereas a circular-shaped metal structure having a thickness of 0.09 mm, fabricated in accordance with the conventional method, cannot pass the tests with respect to the same.
In Table 1, both a circular-shaped metal structure fabricated in accordance with the present invention and a circular-shaped metal structure fabricated in accordance with a conventional method, that is, drawing are tested with respect to a uniformity in a thickness, a straightness and a hardness. A total estimate in the column D was made taking the results of the tests in the columns A, B and C into consideration. A circle (◯) in the column D indicates that the circular-shaped metal structure is practically usable, and a cross (X) in the column D indicates the circular-shaped metal structure is practically unusable.
As is obvious in view of Table 1, a thin-walled circular-shaped metal structure fabricated in accordance with the conventional method has to have a thickness of 0.10 mm or greater in order to be practically usable. Even if a circular-shaped metal structure having a thickness of 0.09 mm or smaller is fabricated in accordance with the conventional method, the circular-shaped metal structure cannot be practically usable.
In contrast, as is obvious in view of Table 1, the present invention can provide a circular-shaped metal structure having a thickness in the range of 0.03 mm to 0.10 mm both inclusive, which is practically usable.
Thus, the present invention makes it possible to fabricate a circular-shaped metal structure having a thickness of 0.09 mm or smaller, which could not be fabricated in accordance with the conventional method.
It is preferable that the method further includes the step (c) of annealing the pipe, the step (c) being to be carried out between the steps (a) and (b).
It is preferable that the method further includes the step (d) of cutting opposite ends of the pipe, the step (d) being to be carried out subsequently to the step (b).
It is preferable that the method further includes the step (e) of annealing the pipe, the step (e) being to be carried out subsequently to the step (d).
The plastic-workable metal may be selected from a stainless steel, a rolled nickel, a nickel alloy, titanium, a titanium alloy, tantalum, molybdenum, hastelloy, permalloy, a marageing steel, aluminum, an aluminum alloy, copper, a copper alloy, pure iron or a steel.
In the specification, unless explicitly indicated, the term xe2x80x9cpipexe2x80x9d covers a pipe having a bottom and a pipe having no bottom.
In still another aspect of the present invention, there is provided an apparatus for fabricating a circular-shaped metal structure, including (a) a pipe rotator which rotates a pipe around an axis thereof, the pipe being composed of a plastic-workable metal, (b) a jig for carrying out drawing, (c) a first device which moves the jig in a direction perpendicular to the axis of the pipe, and (d) a second device which moves the jig in a direction parallel to the axis of the pipe.
The above-mentioned circular-shaped metal structure can be fabricated by means of the apparatus, and the above-mentioned method can be carried out through the apparatus.
The jig may be designed to have a tip end having an acute angle or may be comprised of a roller.
The above-mentioned circular-shaped metal structure may be used as a photosensitive drum or a fixing belt to be used in an electrophotographic printer.
In yet another aspect of the present invention, there is provided a roller assembly including (a) at least two rollers arranged such that axes of the rollers are directed in parallel to each other, and (b) a belt wound around the rollers, the belt being comprised of a circular-shaped metal structure fabricated by plastic working and having a thickness equal to or smaller than 0.09 mm.
There is further provided a roller assembly including (a) at least two rollers arranged such that axes of the rollers are directed in parallel to each other, and (b) a belt wound around the rollers, the belt being comprised of a circular-shaped metal structure to be fabricated by a method including the steps of (a) rotating a pipe around an axis thereof, the pipe being composed of a plastic-workable metal, and (b) applying drawing to an outer wall of the pipe with the pipe being kept rotated, to reduce a wall thickness of the pipe and lengthen a wall of the pipe.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
A printing technology in a printer or copier has remarkably developed. For instance, any document can be copied in full color. Hence, a black-and-white printer or copier will be required to have higher definition in the future, and a color printer or copier will be required to have a high quality and a high printing speed, and to be fabricated in a smaller cost. A photosensitive drum and a thermal fixing section are important keys to meet with such requirements.
In a thermal fixing roller or film, it is required to have a nip area as wide as possible in order to enhance a thermal coefficient and have a qualified image, regardless of whether a thermal fixing roller or film is of a belt type or a thin-walled sleeve type. In response to such requirement, a thin-walled circular-shaped metal structure fabricated in accordance with the invention can be used as a belt or sleeve having a high elasticity, high mechanical strength, and high resistance to fatigue.
The circular-shaped metal structure fabricated in accordance with the invention has higher durability, higher resistance to heat, higher rigidity and longer lifetime than those of a belt composed of resin or nickel, fabricated in accordance with the conventional method. The circular-shaped metal structure fabricated in accordance with the invention may be used as a belt. Hence, it will be possible to downsize a printer or copier by using the circular-shaped metal structure fabricated in accordance with the invention, as a belt, in place of a conventional roller or sleeve having a relatively great thickness.
In addition, the circular-shaped metal structure has a high thermal conductivity and a small thermal capacity. Accordingly, when the circular-shaped metal structure is used as a fixing drum, the fixing drum can be rapidly warmed up. Thus, a period of time for fixation can be shortened. In addition, the fixing drum would have a high thermal conductivity, resulting in reduction in power consumption, and hence, significant cost down.
For instance, the circular-shaped metal structure fabricated in accordance with the invention may be used as a belt in a photosensitive drum. Since a stainless steel of which the circular-shaped metal structure is made would have an enhanced strength by being spun, it would be possible to enhance a flatness and rigidity between axes when a tension force is applied to the circular-shaped metal structure used as a belt, in comparison with a conventional belt composed of resin.
In addition, when the circular-shaped metal structure is used as a belt, since the circular-shaped metal structure has a high Young""s modulus, it would be possible to eliminate non-uniformity in rotation caused by extension and/or extraction, unlike a conventional belt composed of resin. As a result, an accuracy in feeding could be enhanced, ensuring qualified images.
Most of conventional photosensitive drums are comprised of a big cylinder composed of aluminum. It would be possible to downsize a printer or copier by using the circular-shaped metal structure as a belt in place of such a conventional photosensitive drum. Furthermore, it would be possible in a color printer or copier to shorten a period of time in which a sheet passes a plurality of photosensitive drums associated with different colors such as red, green and blue, ensuring a high speed and reduction in a weight, and saving a space.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.